alpha over node is adding to the foreground artifact that is not in the background
I'm not really sure what you're trying to do, sorry.  This might help, might not: https://uvassociates.in/sites/default/files/resize/remote/c0631e46351ca76e7380488b072beb7f-400x312.png

It makes a mesh invisible and just renders the light from it.  It's an older version of Blender, so may not work.  GL